This invention relates to an endoscope apparatus, and, more particularly, to an endoscope apparatus for observing a body cavity by means of a solid-state image sensor.
Recently an endoscope designed to visibly photograph an observed spot by means of a solid-state image sensor has been proposed. Ordinarily, the solid-state image sensor converts an optical image brought to the light-receiving plane into electrical signals by scanning the optical image in a prescribed direction. The signals are treated by, for example, a video processing circuit and then displayed as a visible image on a monitor. If the above-mentioned type of solid-state image sensor is exposed to an intense light, then an electric charge overflows, causing blue streaks to run in the direction in which an image to be displayed on the monitor is scanned; namely, giving rise to the occurrence of the so-called blooming phenomenon.
Ordinarily, the plane of the distal aspect of an endoscope insertion section is provided with an observation window and illumination window juxtaposed with one another, and also with an air/water nozzle for cleaning the observation window. When water droplets are left, after washing, in a space defined between the observation and illumination windows, part of the light beams emitted from the illumination window directly enters into the observation window via the water droplets. In this case, some portions of the light-receiving plane of the solidstate image sensor are exposed to excessive amounts of light, giving rise to the aforementioned blooming phenomenon. In other words, when part of the monitor screen receives excessively large quantities of light, the entire scanning area, including those portions exposed to excessive illumination, gives evidence of the blooming phenomenon. This event leads to drawbacks such that the observation area on the monitor screen is too much reduced for satisfactory image pickup, and, moreover, that retention of the above-mentioned water droplets blurs whatever image is picked up.